The present invention relates to spectacle frames.
In particular, the present invention relates to spectacle frames which have been subjected to galvanic surface treatments.
Spectacle frames normally comprise a plurality of elements or components, such as the earpieces, rims, bridge, double bridge and other parts, which are made of metal, such as steel, stainless steel, bronze, nickel silver, Monel metal and other alloys.
Such frames have a stratiform coating designed to protect the metal below in cathodic fashion, extending the life of the frames, and at the same time giving the frames a desired appearance.
At present, the coating normally consists of a layer of nickel, designed to protect the material below and, simultaneously, to form a particularly smooth outer surface without any roughness from processing. This layer of nickel is covered with a finishing layer made of palladium, gold, chrome or another material which gives the frames the desired appearance. A layer of varnish may be applied to the latter, metal layer.
However, these coatings on spectacle frames have the disadvantage of releasing an excessive amount of nickel, with the risk of causing health problems for the spectacles wearer.
Moreover, in these conventional frames the corrosion strength obtained with such a coating is not strong enough, except in the case of excessively thick coatings. Therefore, the frame production costs are too high.
These corrosion problems are mainly due to the fact that the layer of nickel is quite rigid, and, when the frames are subject to elastic deformation, it tends to develop cracks or fissures in the coating, which allow the penetration of corrosive agents.
To overcome these problems, the present invention provides spectacle frames, as described in claim 1, comprising a plurality of frame elements, such as the earpieces and means which support the lenses, in which the frame elements consist of a core, preferably made of a metal material, and a stratiform coating. The frames are characterised in that the stratiform coating comprises a layer of copper. This layer of copper fully or partially substitutes the nickel layer used on conventional frames. This copper layer not only provides good corrosion strength, but also prevents all the harmful effects caused by the release of nickel in conventional frames.
According to a particularly advantageous aspect, described in claim 2, the coating also comprises a layer of silver, which is applied on top of the layer of copper.
This coating configuration allows optimum protection against corrosion.
The copper and silver layers allow the obtainment of a particularly homogeneous and elastic coating, which follows bending deformation of the frame parts without cracking or splitting. Thus, a particularly compact and even coating is obtained, which is free of cracks and fissures.
As a result, penetration by external corrosive agents is impossible. Optimum protection is obtained for the material which forms the core of the frames.
The other claims describe other advantageous aspects of the present invention.
In particular, the thickness of the layer of copper is between 0.1xcexc and 15xcexc, preferably between 5xcexc and 10xcexc, whilst the layer of silver, in turn, is between 0.1xcexc and 15xcexc thick, preferably between 5xcexc and 10xcexc.
The corrosion strength of the present coating is also advantageous thanks to the fact that the difference in potential, evaluated in conditionsxe2x80x94described in more detail belowxe2x80x94simulating a condition of use of the frames, between the layer of copper and the layer of silver is less than 200 millivolts.
Therefore, partly thanks to this, the corrosion strength of the frames with this coating is particularly high.
The layer of silver, applied on top of the layer of copper, may be covered with one or more layers whose purpose is mainly decorative.
A layer of gold is, therefore, preferably applied over the layer of silver.
Said layer of gold is preferably between 0.1xcexc and 2xcexc thick.
Again, the corrosion strength of such a coating is particularly high, thanks to the fact that the difference in potential, evaluated in conditionsxe2x80x94described in more detail belowxe2x80x94simulating a condition of use of the frames, between the layer of silver and the layer of gold is less than 200 millivolts.
In order to obtain frames with a light grey colour, a layer of palladium is also applied, which may be deposited on top of the layer of gold or, if necessary, on top of the layer of silver.
The layer of palladium is preferably between 0.1xcexc and 2xcexc thick.
For frames which are a darker shade of grey, another layer, of ruthenium, preferably between 0.1xcexc and 0.2xcexc thick, is applied over the layer of palladium.
From the potentiostatic viewpoint, the present invention achieves a difference in potential between each layer and the next which is less than 200 millivolts.
These static potential values for the materials, which form the various layers in the present coating, were measured using the materials and methods of CASS corrosion tests or corrosion tests with artificial perspiration. These tests are well known to experts in the field and, therefore, do not require detailed descriptions here.
In this way, given the low difference in potential between the layers of the coating, protection against corrosion is optimum. In comparison with the layer of copper, the layer of silver has a rather low difference in potential, which gives this combination of layers significant corrosion strength.
In an alternative embodiment, the layer of palladium is applied directly to the layer of copper. In this case, the coating obtained not only eliminates the problem of nickel release, but also has a higher corrosion strength than that of known nickel and palladium coatings used before now.
In yet another embodiment, a thin layer of goldxe2x80x94around 0.1xcexc thickxe2x80x94is applied to the layer of copper, protecting the layer of copper from oxidation, which may occur before the other, final layers in the coating can be applied. Until now, the use of a layer of copper, forming the main layer of the protective and decorative coating, was hindered by the fact that this material was easily oxidisable and, therefore, did not allow any significant wait, as often occurs in industrial processes, for the application of further decorative layers of coating.
The surface of the present coating can also be covered with a layer of varnish or similar material. The varnish may be epoxy or polyester, transparent or coloured.
The technical features of the present invention and the different advantageous aspects are described more clearly in the detailed description which follows, with reference to the preferred application examples, without limiting the scope of the invention.